Age and Ageing (1976), 5, 116
RED-BLOOD-CELL POTASSIUM AND HAND-GRIP STRENGTH IN HEALTHY ELDERLY PEOPLE M. BAHEMUKA AND H. M. HODKINSON
Department of Geriatrics, Northwick Park Hospital, Harrow, Middlesex
Red-blood-cell potassium (RBCK) as an indicator of body potassium status was measured in 103 healthy elderly subjects over the age of 65 years. There was no correlation between RBCK and grip strength. The only significant predictors of grip strength were age and sex. The RBCK values formed a single normal distribution. There was no hypokalaemic subpopulation such as would be expected if potassium deficiency were common in these old people. INTRODUCTION
There is very little information available on the assessment of body potassium status in elderly subjects either in health or disease. Judge (1968) studied the frequency of potassium deficiency in geriatric in-patients by measuring their serum potassium levels. However, it is known that serum potassium is an unreliable estimate of changes in body potassium status. Reliance on symptoms of potassium deficiency is misleading since a considerable degree of deficit often exists without any symptoms of potassium deficiency (Edmonds & Jasani 1972). Electrocardiographs changes expected in potassium deficiency are too non-specific to be of any diagnostic help and correlate poorly with potassium deficiency (British Medical Journal Editorial, 1967). Positive correlation of hand-grip strength and body-potassium status in old people has been reported (Judge & Cowan 1971) but serum potassium and potassium intake were the only estimates of body potassium. In view of the unreliability of serum potassium levels as an indicator of changes in body potassium, we have studied the relationship of hand-grip strength of ambulant healthy elderly people to red-blood-cell potassium. Evidence that red-blood-cell potassium is a better and more reliable practical indicator of changes of body potassium status than serum potassium has been presented elsewhere (Bahemuka & Hodkinson 1976). Subjects and Methods Subjects The subjects of the study were healthy elderly individuals living at home and forming part of a random community sample. All gave full consent to the study. A total of 103 subjects took part, 60 men and 43 women and their average age was 75 years, all being over 65. All subjects were shown to be mentally normal on assessment with a simple questionnaire test of orientation and memory (Hodkinson 1972). This was thought to be of importance, since mental impairment as measured by a similar questionnaire has been shown to be a powerful predictor of grip strength in elderly subjects (Denham et al., 1973). In addition to this safeguard, care was taken to exclude
Downloaded from http://ageing.oxfordjournals.org/ at RMIT University Library on July 17, 2015
Summary
Red-blood-cell Potassium and Hand-grip Strength
117
from further analyses any subject having disabilities likely to affect grip strength such as rheumatoid arthritis or severe osteoarthritis of the hands or old stroke or Colles' fracture. Similarly, subjects were excluded if on medication likely to affect potassium status such as digitalis (Bahemuka & Hodkinson 1976), diuretics, laxatives or potassium supplements. Methods Blood specimens were obtained by venepuncture at approximately 10 a,m. and were divided into three parts for the following measurements: 1. Serum potassium 2. Haematocrit volume (PCV) 3. Whole-blood potassium.
RRPK — ^ x wnole-blood potassium — [serum potassium x (1 — PCV)] PCV (haematocrit) This method of determination of RBCK was found to have a coefficient of variation of 0.70%. Grip strength was measured by the Meredidi dynamometer, taking die average of three readings for the dominant hand. All determinations were carried out in die morning between 10 a.m. and noon. RESULTS
Altogether there were 94 subjects remaining after the exclusions referred to above. Grip strength was entered against the factors to be examined as potential predictors (age, sex, serum potassium and red-cell potassium) in a 'step-down' multiple-regression analysis. This led to the retention of only age and sex as significant predictors (P< 0.001 for each). Serum potassium and red-cell potassium failed to make any significant contribution. Further analyses with the sexes separated confirmed these findings, age then being the only significant predictor. The red-cell potassium results were found to be normally distributed (Fig. 1). There was no suggestion of the existence of a hypokalaemic sub-group such as might have been expected were potassium deficiency common in elderly patients. DISCUSSION
Our results give no support for the view that potassium deficiency is common among elderly subjects. This contrasts with the views of Judge (1968), whose conclusions were however based on serum potassium in elderly in-patients. Our study fails also to confirm the relationship between grip strength and potassium status suggested by Judge & Cowan (1971). They found a correlation between grip strength and potassium intake but not serum potassium levels in a sample of the elderly in the community. Our study merely confirms that age and sex were significant predictors of grip strength; men having stronger grips than women and the younger than the old. Our subjects were all resident in the London Borough of Harrow where social factors are generally more favourable than in many other boroughs. Our failure to find evidence
Downloaded from http://ageing.oxfordjournals.org/ at RMIT University Library on July 17, 2015
Serum potassium and the haematocrit were measured in the usual way by flame photometry and the Coulter S counter respectively. Whole-blood potassium was measured using 1:3 dilution of heparinized blood in de-ionized water. Potassium was then measured in triplicate by flame photometry after a microscopic check that haemolysis was complete. The red-blood-cell potassium (RBCK) was then derived by the following calculation:
M. Bahemuka and H. M. Hodkinson
118
_ 100 "o B
e
-
90-
2.5
50.0
97.5
99.5
Cumulative probability percentage
Fig. 1. Distribution of resulte for red-blood-cell potassium of potassium deficiency might be due to this difference if deficiency were only a feature of more socially disadvantaged communities. Nevertheless, hand-grip strength cannot be recommended as an index of potassium status in well elderly subjects. Measurement of RBCK is a simple and practical alternative which is far more reliable than serum potassium levels (Bahemuka & Hodkinson 1976). ACKNOWLEDGEMENTS
The authors wish to thank the service sections of the Divisions of Clinical Chemistry and Haematology, Northwick Park Hospital and Clinical Research Centre for the estimations of serum potassium and haematocrit respectively. M.B. is grateful to the Division of Clinical Chemistry for being allowed access to the equipment for the determination of whole-blood potassium. REFERENCES
M. & HODKTNSON, H. M. (1976) Red-blood-cell potassium as a practical index of potassium status in elderly patients. Age & Ageing 5, 24-30. British Medical Journal (1967) Editorial: Potassium deficiency in ambulant patients. 1, 191. DHNHAM, M. J., HODKINSON, H. M. & QURESHI, K. N. (1973) Loss of grip in the elderly. Gerontol. Clin. 15, 268-71. EDMONDS, C. J. & JASANI, B. (1972) Total body potassium in hypertensive patients during prolonged diuretic therapy. Lancet ii, 8-12. HODKINSON, H. M. (1972) Evaluation of a mental test score for assessment of mental impairment in the elderly. Age & Ageing, 1, 233-8. JUDGE, T. G. (1968) Hypokalaemia in the elderly. Gerontol. Clin. 10, 102-7. JUDGE, T. G. & COWAN, N. R. (1971) Dietary potassium intake and grip strength in the older people. Gerontol. Clin. 13, 221-6. BAHEMUKA,
Requests for reprints should be sent to H. M. Hodkinson, Nortktoick Park Hospital, Harrow, Middlesex HA1 3UJ.
Downloaded from http://ageing.oxfordjournals.org/ at RMIT University Library on July 17, 2015
0.5
RED-BLOOD-CELL POTASSIUM AND HAND-GRIP STRENGTH IN HEALTHY ELDERLY PEOPLE M. BAHEMUKA AND H. M. HODKINSON
Department of Geriatrics, Northwick Park Hospital, Harrow, Middlesex
Red-blood-cell potassium (RBCK) as an indicator of body potassium status was measured in 103 healthy elderly subjects over the age of 65 years. There was no correlation between RBCK and grip strength. The only significant predictors of grip strength were age and sex. The RBCK values formed a single normal distribution. There was no hypokalaemic subpopulation such as would be expected if potassium deficiency were common in these old people. INTRODUCTION
There is very little information available on the assessment of body potassium status in elderly subjects either in health or disease. Judge (1968) studied the frequency of potassium deficiency in geriatric in-patients by measuring their serum potassium levels. However, it is known that serum potassium is an unreliable estimate of changes in body potassium status. Reliance on symptoms of potassium deficiency is misleading since a considerable degree of deficit often exists without any symptoms of potassium deficiency (Edmonds & Jasani 1972). Electrocardiographs changes expected in potassium deficiency are too non-specific to be of any diagnostic help and correlate poorly with potassium deficiency (British Medical Journal Editorial, 1967). Positive correlation of hand-grip strength and body-potassium status in old people has been reported (Judge & Cowan 1971) but serum potassium and potassium intake were the only estimates of body potassium. In view of the unreliability of serum potassium levels as an indicator of changes in body potassium, we have studied the relationship of hand-grip strength of ambulant healthy elderly people to red-blood-cell potassium. Evidence that red-blood-cell potassium is a better and more reliable practical indicator of changes of body potassium status than serum potassium has been presented elsewhere (Bahemuka & Hodkinson 1976). Subjects and Methods Subjects The subjects of the study were healthy elderly individuals living at home and forming part of a random community sample. All gave full consent to the study. A total of 103 subjects took part, 60 men and 43 women and their average age was 75 years, all being over 65. All subjects were shown to be mentally normal on assessment with a simple questionnaire test of orientation and memory (Hodkinson 1972). This was thought to be of importance, since mental impairment as measured by a similar questionnaire has been shown to be a powerful predictor of grip strength in elderly subjects (Denham et al., 1973). In addition to this safeguard, care was taken to exclude
Downloaded from http://ageing.oxfordjournals.org/ at RMIT University Library on July 17, 2015
Summary
Red-blood-cell Potassium and Hand-grip Strength
117
from further analyses any subject having disabilities likely to affect grip strength such as rheumatoid arthritis or severe osteoarthritis of the hands or old stroke or Colles' fracture. Similarly, subjects were excluded if on medication likely to affect potassium status such as digitalis (Bahemuka & Hodkinson 1976), diuretics, laxatives or potassium supplements. Methods Blood specimens were obtained by venepuncture at approximately 10 a,m. and were divided into three parts for the following measurements: 1. Serum potassium 2. Haematocrit volume (PCV) 3. Whole-blood potassium.
RRPK — ^ x wnole-blood potassium — [serum potassium x (1 — PCV)] PCV (haematocrit) This method of determination of RBCK was found to have a coefficient of variation of 0.70%. Grip strength was measured by the Meredidi dynamometer, taking die average of three readings for the dominant hand. All determinations were carried out in die morning between 10 a.m. and noon. RESULTS
Altogether there were 94 subjects remaining after the exclusions referred to above. Grip strength was entered against the factors to be examined as potential predictors (age, sex, serum potassium and red-cell potassium) in a 'step-down' multiple-regression analysis. This led to the retention of only age and sex as significant predictors (P< 0.001 for each). Serum potassium and red-cell potassium failed to make any significant contribution. Further analyses with the sexes separated confirmed these findings, age then being the only significant predictor. The red-cell potassium results were found to be normally distributed (Fig. 1). There was no suggestion of the existence of a hypokalaemic sub-group such as might have been expected were potassium deficiency common in elderly patients. DISCUSSION
Our results give no support for the view that potassium deficiency is common among elderly subjects. This contrasts with the views of Judge (1968), whose conclusions were however based on serum potassium in elderly in-patients. Our study fails also to confirm the relationship between grip strength and potassium status suggested by Judge & Cowan (1971). They found a correlation between grip strength and potassium intake but not serum potassium levels in a sample of the elderly in the community. Our study merely confirms that age and sex were significant predictors of grip strength; men having stronger grips than women and the younger than the old. Our subjects were all resident in the London Borough of Harrow where social factors are generally more favourable than in many other boroughs. Our failure to find evidence
Downloaded from http://ageing.oxfordjournals.org/ at RMIT University Library on July 17, 2015
Serum potassium and the haematocrit were measured in the usual way by flame photometry and the Coulter S counter respectively. Whole-blood potassium was measured using 1:3 dilution of heparinized blood in de-ionized water. Potassium was then measured in triplicate by flame photometry after a microscopic check that haemolysis was complete. The red-blood-cell potassium (RBCK) was then derived by the following calculation:
M. Bahemuka and H. M. Hodkinson
118
_ 100 "o B
e
-
90-
2.5
50.0
97.5
99.5
Cumulative probability percentage
Fig. 1. Distribution of resulte for red-blood-cell potassium of potassium deficiency might be due to this difference if deficiency were only a feature of more socially disadvantaged communities. Nevertheless, hand-grip strength cannot be recommended as an index of potassium status in well elderly subjects. Measurement of RBCK is a simple and practical alternative which is far more reliable than serum potassium levels (Bahemuka & Hodkinson 1976). ACKNOWLEDGEMENTS
The authors wish to thank the service sections of the Divisions of Clinical Chemistry and Haematology, Northwick Park Hospital and Clinical Research Centre for the estimations of serum potassium and haematocrit respectively. M.B. is grateful to the Division of Clinical Chemistry for being allowed access to the equipment for the determination of whole-blood potassium. REFERENCES
M. & HODKTNSON, H. M. (1976) Red-blood-cell potassium as a practical index of potassium status in elderly patients. Age & Ageing 5, 24-30. British Medical Journal (1967) Editorial: Potassium deficiency in ambulant patients. 1, 191. DHNHAM, M. J., HODKINSON, H. M. & QURESHI, K. N. (1973) Loss of grip in the elderly. Gerontol. Clin. 15, 268-71. EDMONDS, C. J. & JASANI, B. (1972) Total body potassium in hypertensive patients during prolonged diuretic therapy. Lancet ii, 8-12. HODKINSON, H. M. (1972) Evaluation of a mental test score for assessment of mental impairment in the elderly. Age & Ageing, 1, 233-8. JUDGE, T. G. (1968) Hypokalaemia in the elderly. Gerontol. Clin. 10, 102-7. JUDGE, T. G. & COWAN, N. R. (1971) Dietary potassium intake and grip strength in the older people. Gerontol. Clin. 13, 221-6. BAHEMUKA,
Requests for reprints should be sent to H. M. Hodkinson, Nortktoick Park Hospital, Harrow, Middlesex HA1 3UJ.
Downloaded from http://ageing.oxfordjournals.org/ at RMIT University Library on July 17, 2015
0.5
